Intercom system for mansion/apartment house

ABSTRACT

An intercom system for mansion/apartment house of the present invention can achieve the power saving by suppressing a current consumption at the time of calling by a visitor standing at a main entrance or a residential front door or at the time of locking or releasing an electric door lock which is mounted on a front door of the main entrance and can ensure the favorable talk quality by suppressing howling. To a common bus, at least one main entrance station including a talk module for performing calling and talking and at least one switch module being connected to the talk module and having a call switch for performing selecting of a station, a bus controller for supplying a power to a common bus, and a plurality of residential master stations for performing calling and talking with the main entrance station are connected in parallel respectively. The bus controller comprises an impedance increasing circuit for increasing an output impedance to a high impedance and the talk module of the main entrance station and respective residential master station respectively comprise load resistances which are connected to the common bus.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] The present invention relates to an intercom system for mansion/apartment house, and more particularly to an intercom system for mansion/apartment house which can achieve a power saving by suppressing current consumption and, at the same time, can ensure the favorable talking quality by preventing the occurrence of howling.

[0003] (2) Description of the Related Art

[0004] Conventionally, as this type of an intercom system for mansion/apartment house, there has been proposed an intercom system for mansion/apartment house which has a structure shown in a block diagram of FIG. 3.

[0005] The intercom system for mansion/apartment house shown in the drawing has at least one main entrance station 101 (101, 101, . . . ), a plurality of residential master stations 102, 102, . . . which are respectively installed in the inside of a plurality of residences in a mansion/apartment house, a common bus 103 which is served for connecting the main entrance station 101 and respective residential master stations 102, 102, . . . in parallel, a bus controller 104 which is served for supplying a direct current power supply (DC power supply) to the main entrance station 101 and respective residential master stations 102, 102, . . . which are connected in parallel through the common bus 103, an electronic door lock 105 (105, 105, . . . ) which is connected to the main entrance station 101 for locking and releasing an entrance door of a mansion/apartment house, and a plurality of call switches 106, 106, . . . which are connected to respective residential master stations 102, 102, . . . which, are mounted to front doors of respective residences (hereinafter referred to as “residential front doors”) and are operated by a visitor who makes calling.

[0006] In the drawing, the main entrance station 101 comprises a talk module 110 which includes a control circuit 120, an impedance increasing circuit 121, a multiplex/separation circuit 122, a speech circuit 123, a data transmission/reception circuit 124, an electric door lock circuit 125, an electric door drive circuit 126 and a power supply circuit 127, and at least one switch module 111 which includes a control circuit 130, a call switch 131, and a lighting circuit 132.

[0007] Further, each residential master station 102, 102, . . . includes a control circuit 140, an impedance increasing circuit 141, a multiplex/separation circuit 142, a speech circuit 143, an electric door lock releasing button 144, a data transmission/reception circuit 145 and a power supply circuit 146.

[0008] Further, the bus controller 104 includes a power supply circuit 150 and an impedance increasing circuit 151.

[0009] In the intercom system for mansion/apartment house having such a structure, the impedance increasing circuit 151 of the bus controller 104 supplies a stabilized direct current power supply such as DC 24V, for example, to the common bus 103 through the power supply circuit 150. This direct current power supply is supplied as a standby operational power supply to the power supply circuit 127 through the impedance increasing circuit 121 of the talk module 110 which forms the main entrance station 101 and to the power supply circuits 146 through the impedance increasing circuits 141 of respective residential master stations 102, 102, . . . .

[0010] Here, when a visitor standing at the entrance of the mansion/apartment house operates the call switch 131 of the switch module 111 which forms the main entrance station 101 to call a resident living in a specified residence, a calling data signal outputted from a control circuit 130 which detects this calling operation is transmitted to respective residential master stations 102, 102, . . . through the control circuit 120, the data transmission/reception circuit 124, the multiplex/separation circuit 122 of the talk module 110 and the common bus 103.

[0011] Here, in respective residential master stations 102, 102, . . . , the control circuit 140 compares an address which forms the calling data signal which is received through the common bus 103, the multiplex/separation circuit 142 and the data transmission/reception circuit 145 with a preset address at its own terminal. If these addresses agree with each other, the control circuit 140 generates a calling tone by means of a speaker (not shown in the drawing) which forms the speech circuit 143 so that the calling from the visitor standing at the entrance of the mansion/apartment house is informed to the resident living in the residence of selected station.

[0012] Subsequently, based on the calling tone generated by the speaker (not shown in the drawing) which forms the speech circuit 143 of the residential master station 102, when the resident living in the residence who confirmed the selection of station by the visitor standing at the entrance of the mansion/apartment house picks up a handset (not shown in the drawing) which forms the speech circuit 143, due to the control of the control circuit 140 which detects this response operation, the speech function (detailed explanation thereof being omitted) of the speech circuit 143 is activated and the response data signal outputted from the control circuit 140 is transmitted to the talk module 110 which forms main entrance station 101 through the data transmission/reception circuit 145, the multiplex/separation circuit 142 and the common bus 103.

[0013] Further, in the speech module 110 which forms the main entrance station 101, the control circuit 120 detects the response data signal which is received through the common bus 103, the multiplex/separation circuit 122 and the data transmission/receptions circuit 124 and activates the speech function (detailed explanation thereof being omitted) of the speech circuit 123. Accordingly, a speech path (detailed explanation being omitted) is established between a microphone and a speaker (not shown in the drawing) which form the speech circuit 123 and the handset (not shown in the drawing) of the speech circuit 143 of the residential master station 102 which is called as the selected station and hence, the talk is established by transmitting and receiving speech signals through this speech path.

[0014] Subsequently, when the resident living in the residence which is called as the selected station operates the electric door lock releasing button 144 of the residential master station 102 for releasing the electric door lock 105 mounted on the front door at the main entrance, a release data signal outputted from the control circuit 140 which detects this releasing operation is transmitted to the control circuit 120 of the talk module 110 which forms the main entrance station 101 through a path similar to the path for the above-mentioned response data signal.

[0015] Further, the control circuit 120 of the talk module 110 which forms the main entrance station 101 and detects the releasing operation by the resident living in the residence which is called as the selected station based on the lock release data signal transmitted from the residential master station 102 controls the electric door lock drive circuit 126 so as to drive the electric door lock circuit 125 thus releasing the electric door lock 105.

[0016] However, in the conventional intercom system for mansion/apartment house, the impedance increasing circuit 151 of the bus controller 104 has given frequency characteristics and hence, when the speech signals for establishing the talk are transmitted to the common line 103, the frequency characteristics which the impedance increasing circuit 151 also influences a feedback quantity of the speech signals so that it is difficult to sufficiently cancel the feedback speech signals at the speech circuit 123 of the talk module 110 which forms the main entrance station 101 and at the speech circuit 143 of the residential master station 102 which is called as the selected station whereby there exists a drawback that the howling is liable to be generated.

[0017] Further, in the impedance increasing circuit 121 of the talk module 110 which forms the main entrance station 101 and in the impedance increasing circuits 141 of respective residential master stations 102, 102, . . . , the power supply voltage to the bus controller 104 is set to a high value to ensure a dynamic range with a standby current value. At the same time, the electric door lock circuit 125 of the talk module 110 which forms the main entrance station 101 is driven at a stabilized low-level voltage through the electric door lock drive circuit 126 based on the control by the control circuit 120 so as to lock and release the electric door lock 105. Accordingly, there has been a drawback that the current consumption in the talk module which is operated with the power supply which is stabilized through the power supply circuit 127, for example, the power supply of DC 5V is increased.

[0018] Further, when the call switch 106 mounted at the residential front door is operated, the calling tone is generated by the speaker (not shown in the drawing) which forms the speech circuit 143 based on the control of the control circuit 140 of the residential master station 102 which detects the calling operation. Accordingly, there has been a drawback that the current consumption in the residential master station which is operated with the power supply which is stabilized through the power supply circuit 146, for example, the power supply of DC 5V is increased.

[0019] The present invention has been made to solve the above-mentioned drawbacks and it is an object of the present invention to provide an intercom system for mansion/apartment house which can achieve the power saving by suppressing current consumed at the time of calling initiated by a visitor standing at a main entrance of a mansion/apartment house or a residential front door or at the time of releasing an electric door lock mounted on a front door of the main entrance of the mansion/apartment house and, at the same time, can ensure the favorable talk quality by suppressing the howling.

SUMMARY OF THE INVENTION

[0020] To achieve the above-mentioned object, in an intercom system for mansion/apartment house according to the present invention which connects at least one main entrance station including a talk module for performing calling and talking and at least one switch module being connected to the talk module and having a call switch for performing selecting of a station, a bus controller for supplying a power to a common bus, and a plurality of residential master stations for performing calling and talking with the main entrance station to the common bus in parallel respectively, wherein in that the bus controller comprises an impedance increasing circuit for increasing an output impedance to a high impedance, the talk module of the main entrance station comprises a speech circuit having a load resistance which is connected to the common bus, and each residential master station comprises a speech circuit having a load resistance which is connected to the common bus.

[0021] According to the intercom system for mansion/apartment house having such a structure, by connecting the speech circuits having the load resistances in series with the impedance increasing circuit of the talk module which forms the main entrance station and the impedance increasing circuits of respective residential master stations which are connected to the common bus in parallel, it becomes possible to sufficiently cancel the feedback tone signals without receiving the influence of the alternating current impedance which the common bus has so that the generation of howling can be prevented.

[0022] Further, in the intercom system for mansion/apartment house of the present invention, the talk module of the main entrance station and the residential master stations are respectively provided with impedance increasing circuits for increasing input impedance at the standby state to a high impedance and the impedance increasing circuits are respectively provided with fixed voltage circuits.

[0023] According to the intercom system for mansion/apartment house having such a structure, when the main entrance station and the residential master stations receive supplied the direct current power supply from the bus controller, the impedance increasing circuits respectively perform constant-current operations due to controls performed by the fixed voltage circuits and hence, even when the main entrance station, the residential master station and the bus controller are connected to the common bus in parallel, the lowering of the alternating impedance which the common bus has can be prevented.

[0024] Further, in the intercom system for mansion/apartment house of the present invention the impedance increasing circuit of the bus controller is provided with a frequency calibration circuit.

[0025] According to the intercom system for mansion/apartment house having such a structure, respective impedance in a high range and a low range can be suppressed by the frequency calibration circuit which is connected to the impedance increasing circuit of the bus controller in parallel and hence, even when the frequency of the direct current power supply becomes high, the output impedance to the common bus can be increased up to a given impedance.

[0026] Further, in the intercom system for mansion/apartment house of the present invention, the talk module of the main entrance station comprises a constant-current electric door lock drive circuit for driving an electric door lock circuit which locks and releases an electric door lock.

[0027] According to the intercom system for mansion/apartment house having such a structure, the power supply to the constant-current electric door lock drive circuit of the talk module which forms the main entrance station can be performed such that, without using a low-level voltage which is stabilized in the talk module, the constant-current to be a small current value is supplied based on the direct current power supply from the common bus so as to drive the electric door lock circuit thus locking and releasing the electric door lock whereby the power saving can be achieved.

[0028] Further, each residential master station which forms the intercom system for mansion/apartment house of the present invention comprises a piezoelectric element circuit which generates a calling tone upon operation of a call switch which is installed at a residential front door.

[0029] According to the intercom system for mansion/apartment house having such a structure, the power supply to the piezoelectric element circuit of the residential master station which informs of the operation of the call switch with the generation of call tone can be performed such that, without using a low-level voltage which is stabilized in the residential master station, the constant-current to be a small current value is supplied based on the direct current power supply from the common bus so as to drive the piezoelectric element circuit whereby the power saving can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a block diagram showing the structure of an intercom system for mansion/apartment house according to one embodiment of the present invention.

[0031]FIG. 2 is a circuit block diagram showing the specific structure of the intercom system for mansion/apartment house according to one embodiment of the present invention.

[0032]FIG. 3 is a block diagram showing the structure of a conventional intercom system for mansion/apartment house.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Embodiments of preferred mode for carrying out the present invention to which an intercom system for mansion/apartment house according to the present invention is applied are explained in conjunction with attached drawings.

[0034]FIG. 1 is a block diagram showing the structure of an intercom system for mansion/apartment house according to one embodiment of the present invention. As shown in the drawing, the intercom system for mansion/apartment house comprises at least one main entrance station 1 (1, 1, . . . ) which is installed at an entrance or the like of a mansion/apartment house (hereinafter referred to as “main entrance”), a plurality of residential master stations 2, 2, . . . which are respectively installed in the inside of a plurality of residences in a mansion/apartment house for performing calling and talking with the main entrance station 1, a common bus 3 which is served for connecting the main entrance station 1 and respective residential master stations 2, 2, . . . in parallel, a bus controller 4 which is served for supplying a direct current power supply (DC power supply), for example, DC 24V to the main entrance station 1 and respective residential master stations 2, 2, . . . which are connected in parallel through the common bus 3, an electronic door lock 5 (5, 5, . . . ) which is connected to the main entrance station 1 for locking and releasing an entrance door of a main entrance, and a plurality of call switches 6, 6, . . . being connected to respective residential master stations 2, 2, . . . which are mounted on front doors of respective residences (hereinafter referred to as “residential front doors”) and are operated by a visitor who makes calling.

[0035] In the drawing, the main entrance station 1 comprises a talk module 10 which is connected to the common bus 3 and performs calling and talking and at least one switch module 11 (11, 11 . . . ) which is connected to the talk module 10 and performs station selection calling.

[0036] Further, talk module 10 comprises a control circuit 20 which controls a circuit operation in the inside of the talk module 10, a reactance transistor circuit, i.e. impedance increasing circuit 21 which is connected to the common bus 3 and increases an input impedance in the standby state to a high impedance, for example, 9-10 kΩ, a multiplex/separation circuit 22 which establishes a signal transmission path between the common bus 3 and a speech circuit 23 and a data transmission/reception circuit 24 which will be described later and multiplexes or separates various signals (data signals, speech signals and the like) which are transmitted and received, the speech circuit 23 which is controlled by the control circuit 20 and is served for the talking by a visitor at the main entrance, the data transmission/reception circuit 24 which establishes a signal transmission path between the control circuit 20 and the multiplex/separation circuit 22 and transmits and receives various signals, an electric door lock circuit 25 which is connected to the common bus 3 and locks and releases the electric door lock 5, a constant-current electric door lock drive circuit 26 which is served for driving the electric door lock circuit 25 based on the control performed by the control circuit 20, a power supply circuit 27 which is connected to the reactance transistor circuit 21 and is served for supplying an operating power supply to respective circuits in the inside of the talk module 10 except for the electric door lock circuit 25 and the constant-current electric door lock drive circuit 26, and a fixed voltage circuit 28 which is served for ensuring a dynamic range of the reactance transistor circuit 21.

[0037] Further, switch module 11 includes a control circuit 30 which is connected to the control circuit 20 of the talk module 10 and is served for controlling the circuit operation in the inside of the switch module 11, a call switch 31 which a visitor operates to perform the station selection calling at the main entrance, and a lighting circuit 32 which is arranged in parallel to the call switch 31. Here, the control circuit 30 is connected in series with the control circuit 30 (not shown in the drawing) of other switch module 11.

[0038] In the drawing, each residential master station 2, 2, . . . comprises a control circuit 40 which controls a circuit operation in the inside of the residential master station 2, a reactance transistor circuit, i.e. impedance increasing circuit 41 which is connected to the common bus 3 and increases an input impedance in the standby state to a high impedance, for example, 90-100 kΩ, a multiplex/separation circuit 42 which establishes a signal transmission path between the common bus 3 and a speech circuit 43 and a data transmission/reception circuit 45 which will be described later and multiplexes or separates various signals which are transmitted and received, the speech circuit 43 which is controlled by the control circuit 40 and is served for talking by a resident living in the inside of the residence, an electric door lock releasing button 44 which the resident living in the inside of the residence operates to release the electric door lock 5 installed at the main entrance, the data transmission/reception circuit 45 which establishes a signal transmission path between the control circuit 40 and the multiplex/separation circuit 42 and transmits and receives various signals, a piezoelectric element circuit 46 which is connected to the common bus 3 and informs of the operation of the call switch 6, 6 . . . which is installed at the residential front door or the operation of the call switch 31 of the switch module 11 which forms the main entrance station 1 with the generation of a call tone based on the control of the control circuit 40, a power supply circuit 47 which is connected to the reactance transistor circuit 41 and is served for supplying an operating power supply to respective circuits in the inside of the residential master station 2 except for the piezoelectric element circuit 46, and a fixed voltage circuit 48 which is served for ensuring a dynamic range of the reactance transistor circuit 41.

[0039] In the drawing, the bus controller 4 includes a power supply circuit 50 which is served for stabilizing a direct current power supply, a passive reactance circuit, i.e. impedance increasing circuit 51 which is connected with the direct current power supply through the power supply circuit 50 and is served for increasing output impedance to the common bus 3 to a high impedance, for example, 200-300 Ω, and a frequency calibration circuit 52 which is connected to the passive reactance circuit 51 in parallel and is served for calibrating the frequency characteristics which the passive reactance circuit 51 has.

[0040]FIG. 2 is a circuit block diagram of a specific structure of the intercom system for mansion/apartment house according to one embodiment of the present invention.

[0041] In the talk module 10 which forms the main entrance station 1 shown in the drawing, the reactance transistor circuit 21 includes a NPN type transistor Q1 which has a collector thereof connected to the common bus 3, an emitter thereof connected to the power supply circuit 27 through a resistance R1 and a base thereof connected to a resistance R9 of a fixed voltage circuit 28 which will be described later, and resistances R2, R3 which are respectively inserted between the base and the collector and between the base and the emitter of the transistor Q1. Here, a connection point where the resistance R3, the resistance R1 which is connected to the resistance R3 in series and the power supply circuit 27 are connected to each other is referred to as a connection point P1.

[0042] Further, the talk module 23 includes a microphone M1 and a speaker SP1 which establishes talking between a visitor who stands at the main entrance and performs calling by selecting the station and the resident living in the inside of the residence, a microphone amplifier AMP1 which amplifies speech signals which form transmitting tones inputted to the microphone M1, a speaker amplifier AMP2 which is served for amplifying the speech signals which form received tones generated by the speaker SP1, and a NPN type transistor Q2 which has a collector thereof connected to the common bus 3 through a load resistance R4 and a multiplex/separation circuit 22 and connected to the speaker amplifier AMP2 through a capacitance C1 and an adder circuit ADD1, an emitter thereof connected to a reference potential point through a resistance R5 and a base thereof connected to the microphone amplifier AMP1. The adder circuit ADD1 is connected to a connection point between the base of the transistor Q2 and the microphone amplifier AMP1.

[0043] Further, the electric door lock circuit 25 includes an electric door lock switch SW1 which is changed over for locking and releasing the electric door lock 5 and an electric door lock relay RY1 which has both ends thereof respectively connected to the common bus 3 and a collector of a NPN type transistor Q3 of the constant-current electric door lock drive circuit 26 which will be explained later and is turned on or off to change over the electric door lock switch SW1.

[0044] Further, the constant-current electric door lock drive circuit 26 includes the NPN type transistor Q3 which has the collector thereof connected to the electric door lock relay RY1 of the electric door lock circuit 25, an emitter thereof connected to the reference potential point through a resistance R6 and a base thereof connected to the control circuit 20 through a resistance R7. To a connection point disposed between the base of the transistor Q3 and the resistance R7, the reference potential point is connected through a resistance R8.

[0045] Further, the fixed voltage circuit 28 includes a constant-voltage diode ZD1 which has an anode thereof connected to the reference potential point and a cathode thereof connected to the base of the transistor Q1 of the reactance transistor circuit 21 through a protective resistance R9.

[0046] In each residential master station 2 shown in the drawing, the reactance transistor circuit 41 includes a NPN type transistor Q4 which has a collector thereof connected to the common bus 3, an emitter thereof connected to the power supply circuit 47 through a resistance R10 and a base thereof connected to a resistance R17 of a fixed voltage circuit 48 which will be described later, and resistances R11, R12 which are respectively inserted between the base and the collector and between the base and the emitter of the transistor Q4. Here, a connection point where the resistance R12, the resistance R10 which is connected to the resistance R12 in series and the power supply circuit 47 are connected to each other is referred to as a connection point P2.

[0047] Further, the speech circuit 43 includes a handset HS1 in which a microphone M2 and a receiver R1 which establish talking between the resident living in the inside of the residence who is called by selection of station and a visitor who stands at the main entrance are incorporated, a microphone amplifier AMP3 which amplifies speech signals which form transmitting tones inputted to the microphone M2 of the handset HS1, a receiver amplifier AMP4 which is served for amplifying speech signals which form received tones generated by the receiver R1 of the handset HS1, and a NPN type transistor Q5 which has a collector thereof connected to the common bus 3 through a load resistance R13 and the multiplex/separation circuit 42 and connected to the receiver amplifier AMP4 through a capacitance C2 and an adder circuit ADD2, an emitter thereof connected to a reference potential point through a resistance R14 and a base thereof connected to the microphone amplifier AMP3. The adder circuit ADD2 is connected to a connection point between the base of the transistor Q5 and the microphone amplifier AMP3.

[0048] Further, the piezoelectric element circuit 46 includes a PNP type transistor Q6 which has an emitter thereof connected to the common bus 3, a collector thereof connected to a resistance R15 and a base thereof connected to the control circuit 40 respectively, a NPN type transistor Q7 which has an emitter thereof connected to the reference potential point through a resistance R16, a collector thereof connected to the collector of the transistor Q6 through a resistance R15 and a base thereof connected to the control circuit 40 respectively, and a piezoelectric element PD1 which generates call tones. To a connection point between the collector of the transistor Q6 and the resistance R15, one end of the piezoelectric element PD1 which has the other end thereof connected to the reference potential point is connected.

[0049] Further, the fixed voltage circuit 48 includes a constant-voltage diode ZD2 which has an anode thereof connected to the reference potential point and a cathode thereof connected to the base of the transistor Q4 of the reactance transistor circuit 41 through a protective resistance R17.

[0050] In the bus controller 4 shown in the drawing, the passive reactance circuit 51 includes a coil L1. The frequency calibration circuit 52 which comprises a resistance R18 and a capacitance C3 connected in series is inserted between both ends of the coil L1 in parallel.

[0051] The manner of operation of the intercom system for mansion/apartment house according to one embodiment of the present invention having such a structure is explained hereinafter. Here, the explanation of the operation of the lighting circuit 32 of the switch module 11 which forms the main entrance station 1 shown in the block diagram of FIG. 1 is omitted.

[0052] As shown in the block diagram of FIG. 1, the passive reactance circuit 51 of the bus controller 4 supplies the stabilized direct current power supply, for example, DC 24V to the common bus 3 through the power supply circuit 50 and this direct current power supply is supplied as the standby operational power supply to the power supply circuit 27 through the reactance transistor circuit 21 of the talk module 10 which forms the main entrance station 1 installed at the main entrance and to the power supply circuit 47 through the reactance transistor circuit 41 of respective residential master stations 2, 2, . . . which are respectively installed in the inside of a plurality of residences. At the same time, the direct current power supply is received as the operational power supply by the electric door lock circuit 25 of the talk module 10 which forms the main entrance station 1 and the piezoelectric element circuits 46 of respective residential master stations 2, 2, . . .

[0053] Here, as shown in the circuit block diagram shown in FIG. 2, the passive reactance circuit 51 of the bus controller 4 comprises the coil L1 which has given frequency characteristics and hence, when the frequency of the direct current power supply which is stabilized through the power supply circuit 50 becomes high, the output impedance to the common bus 3 is increased in proportion to the frequency characteristics which the coil L1 has so that the transmission loss is generated in the common bus 3. Accordingly, the transmission states of various signals (data signals, speech signals and the like) which are transmitted or received between the talk module 10 which forms the main entrance station 1 and the residential master station 2 which is called by selection of station becomes unstable.

[0054] To solve such a problem, with the provision of the resistance R18 of the frequency characteristic circuit 52 which is connected in parallel between both ends of the coil L1 of the passive reactance circuit 51 of the bus controller 4, the output impedance to the common bus 3 can be suppressed to equal to or less than 300 Ω at the frequency of not less than 2 kHz, for example, while with the provision of the capacitance C3 which is connected in series with the resistance R18, the output impedance to the common bus 3 is suppressed such that the output impedance does not become equal to or less than 200 Ω at the frequency of 800 Hz-2 kHz, for example. Accordingly, even when the frequency of the direct current power supply which is stabilized through the power supply circuit 50 is increased, it becomes possible to maintain the output impedance to the common bus 3 at 200-300 Ω, for example, so that the transmission loss of the common bus 3 can be reduced whereby the transmission states of various signals which are transmitted or received between the talk module 10 forming the main entrance station 1 and respective residential master stations 2 which are connected in parallel to the common bus 3 can be stabilized.

[0055] Further, assume a case in which, due to the above-mentioned control by the frequency calibration circuit 52 of the bus controller 4, the output impedance to the common bus 3 is maintained at 200-300 Ω, for example, without receiving the influence of given frequency characteristics which the coil L1 of the passive reactance circuit 51 has. In such a case, the output voltages from the reactance transistor circuit 21 of the talk module 10 which forms the main entrance station 1 and the reactance transistor circuits 41 of respective residential master stations 2, 2, . . . to the power supply circuits 27, 47 shown in the circuit block diagram of FIG. 2, that is, the voltage levels V1, V2 of the connection points P1, P2 are respectively determined based on currents (collector currents) I1, I2 which flow in common to the reactance transistor circuits 21, 41 and the power supply circuits 27, 47. Accordingly, in the standby state in which the currents 11, 12 are assumed to take small current values, the potential differences (voltage differences) between the collectors and the emitters of the transistors Q1, Q4, that is, the voltage levels of the connection points P1, P2 are small so that the dynamic ranges are small. On the other hand, in the operational state in which the currents I1, I2 are to be large current values, the voltage levels V1, V2 of the connection points P1, P2 become large and hence, the dynamic ranges become large so that it is impossible to ensure the fixed dynamic range.

[0056] To solve such a problem, by allowing the currents I1, I2 to respectively flow into the constant-voltage diodes ZD1, ZD2 of the fixed voltage circuit 28 of the talk module 10 which forms the main entrance station 1 and the fixed voltage circuit 48 of respective residential master stations 2, 2, . . . through the protective resistances R9, R17, even when the current values of the currents I1, I2 are changed, the voltage levels V1, V2 of the connection points P1, P2 respectively take the constant potential so that the constant dynamic range can be ensured and the reactance transistor circuits 21, 41 can perform the constant-current operations.

[0057] Subsequently, in the block diagram shown in FIG. 1 when the visitor standing at the main entrance operates the call switch 31 of the switch module 11 which forms the main entrance station 1 to call the resident living in the specified residence, the call data signals outputted from the control circuit 30 which detects this call operation are transmitted to each residential master station 2, 2, . . . through the control circuit 20, the data transmission/reception circuit 24, the multiplex/separation circuit 22 of the talk module 10 and the common bus 3 shown in the circuit block diagram of FIG. 2.

[0058] Further, in each residential master station 2, 2, . . . , the control circuit 40 compares an address which forms the call data signals received through the common bus 3, the multiplex/separation circuit 42 and the data transmission/reception circuit 45 with an address which is preliminarily set at its own terminal. If these addresses agree with each other, the voltage level of the base of the transistor Q6 of the piezoelectric element circuit 46 is alternately shifted from the Low level to the High level and from the High level to the Low level so as to control the conductive/non-conductive state. At the same time, the voltage level of the base of the transistor Q7 is alternately shifted from the High level to the Low level and the Low level to the High level at the timing equal to the changeover of the level of the transistor Q6 so as to control the non-conductive/conductive state.

[0059] Further, when the transistors Q6, Q7 of the piezoelectric element circuit 46 are respectively controlled to the conductive state and the nonconductive state due to the control circuit 40 of the residential master station 2, the constant current which is to be the small current value based on the direct current power supply, for example, DC 24 V from the common bus 3 is supplied to the piezoelectric element PD1 to make the piezoelectric element PD1 become the ON state. That is, the current is not supplied to the piezoelectric element PD1 from the power supply of the power supply circuit 47 such as the power supply of low level at 5 V. On the other hand, when the transistors Q6, Q7 are respectively controlled to the non-conductive state and the conductive state, the piezoelectric element PD1 becomes the OFF state. By alternately repeating this ON state/OFF state, the call tone can be generated so that the calling from the visitor standing at the main entrance can be informed to the resident living in the residence which forms the selected station without lowering the alternating current impedance of the common bus 3. Further, even when the voltage level of the direct current power supply of the common bus 3 is changed, since the transistors Q6, Q7 absorb the change width of the voltage level, the voltage applied to the piezoelectric element PD1 can be always made constant so that voltage which exceeds the specification is not generated.

[0060] Subsequently, as shown in the circuit block diagram of FIG. 2, when the resident who has confirmed the calling by selection of station from the visitor standing at the main entrance based on the call tone generated by the piezoelectric element PD1 of the piezoelectric element circuit 46 of the residential master station 2 picks up the handset HS1 which forms the speech circuit 43, the speech function of the speech circuit 43 is activated, for example, the microphone amplifier AMP3 and the receiver amplifier AMP4 are activated based on the control performed by the control circuit 40 which detects this response operation and, at the same time, the response data signals from the control circuit 40 are transmitted to the talk module 10 which forms the main entrance station 1 through the data transmission/reception circuit 45, the multiplex/separation circuit 42 and the common bus 3.

[0061] Further, in the talk module 10 which forms a main entrance station 1, the control circuit 20 detects the response data signals which are received through the common bus 3, the multiplex/separation circuit 22 and the data transmission/reception circuit 24 and activates the speech function of the speech circuit 23, that is, activates the microphone amplifier AMP1 and the speaker amplifier AMP2, for example.

[0062] Here, when the visitor standing at the main entrance inputs the transmitting tones to the microphone Ml of the talk module 10 which forms the main entrance station 1 to establish the talking between the visitor and the resident in the inside of the residence which is called by selection of station, the speech signals which are subjected to suitable signal processing is amplified through the microphone amplifier AMP1 and thereafter is transmitted through the base and the collector of the transistor Q2 and the load resistance R4 to the multiplex/separation circuit 22. Here, the combined series resistance value made of the output impedance, 200-300 Ω in this embodiment to the common bus 3 which is increased through the passive reactance circuit 51 of the bus controller 4 and of the load resistance R4, 470 Ω, for example, becomes the transmission load resistance. The speech signals are therefore transmitted to the common bus 3 at the constant output voltage with no transmission loss and are transmitted to the adder circuit ADD1 as feedback tone signals and are transmitted to the adder circuit ADD1 through the base and the collector of the transistor Q2 and the capacitance C1 as the feedback tone signals.

[0063] Further, the adder circuit ADD1 of the talk module 10 which forms the main entrance station 1 can sufficiently cancel the speech signals which forms the transmitting tones which are transmitted through a different path as feedback tone signals without receiving the influence of the alternating current impedance which the common bus 3 has. Accordingly, the output of the feedback tone signals to the speaker SP1 through the speaker amplifier AMP2 can be reduced so that the generation of the howling can be prevented.

[0064] Further, the input impedance of the speech circuit 43 of the residential master station 2 which is called by selection of station is set sufficiently larger than the output impedance to the common bus 3 which is increased through the passive reactance circuit 51 of the bus controller 4, 200-300 Ω in this embodiment. That is, the input impedance is set to 20-30 kΩ. Accordingly, the speech signals can be received as speech signals having the voltage level which is substantially equal to the signal voltage of the speech signals from the main entrance station 1 which are transmitted through the common bus 3 and the multiplex/separation circuit 42. The speech signals are transmitted to the capacitance C2 and the adder circuit ADD2 and are generated as sounds at the receiver R1 of the handset HS1 as the received tones from the visitor standing at the main entrance which is amplified through the receiver amplifier AMP4.

[0065] On the other hand, when the resident in the inside of the residence which is called by selection of station inputs the transmitting tones to the microphone M2 of the handset HS1 of the speech circuit 43 of the residential master station 2 to establish talking between the resident and the visitor standing at the main entrance, the speech signals which are subjected to suitable signal processing are amplified through the microphone amplifier AMP3 and thereafter is transmitted through the base and the collector of the transistor Q5 and the load resistance R13 to the multiplex/separation circuit 42. Here, the combined series resistance value made of the output impedance , 200-300 Ω in this embodiment to the common bus 3 which is increased through the passive reactance circuit 51 of the bus controller 4, and of the load resistance R13, 470 Ω, for example, becomes the transmission load resistance. The speech signals are therefore transmitted to the common bus 3 at the constant output voltage with no transmission loss and are transmitted to the adder circuit ADD2 as the feedback tone signals and are transmitted to the adder circuit ADD2 through the base and the collector of the transistor Q5 and the capacitance C2 as the feedback tone signals.

[0066] Further, the adder circuit ADD2 of the speech circuit 43 of the residential master station 2 can sufficiently cancel the speech signals which are transmitted through a different path as feedback tone signals without receiving the influence of the alternating current impedance which the common bus 3 has so that the output of the feedback tone signals to the receiver R1 of the handset HS1 through the receiver amplifier AMP4 can be reduced whereby the generation of the howling can be prevented.

[0067] Further, the input impedance of the speech circuit 23 of the talk module 10 which forms the main entrance station 1 is set sufficiently larger than the output impedance to the common bus 3 which is increased through the passive reactance circuit 51 of the bus controller 4, 200-300 Ω in this embodiment. That is, the input impedance is set to 60-80 kΩ, for example. Accordingly, the speech signals can be received as speech signals having the voltage level which is substantially equal to the signal voltage of the speech signals from the residential master station 2 which are transmitted through the common bus 3 and the multiplex/separation circuit 22. The speech signals are transmitted to the capacitance C1 and the adder circuit ADD1 and are generated as sounds at the speaker SP1 as the received tones from the resident in the inside of the residence which is called by selection of station and is amplified through the speaker amplifier AMP2.

[0068] Subsequently, as shown in the block diagram of FIG. 1 and the circuit block diagram of FIG. 2, when the resident in the inside of the residence who is called by selection of station operates the electric door lock releasing button 44 of the residential master station 2 to release the electric door lock 5 which is installed at the entrance door of the main entrance, the door lock releasing signal outputted from the control circuit 40 which detects the releasing operation is transmitted to the control circuit 20 of the talk module 10 which forms the main entrance station 1 through a path similar to the path for the above-mentioned response data signals.

[0069] Further, based on the door lock releasing signal from the residential master station 2, the control circuit 20 of the talk module 10 which forms the main entrance station 1 and detects the releasing operation performed by the resident in the inside of the residence who is called by station selection controls the transistor Q3 to the conductive state by shifting the voltage level of base of the transistor Q3 from the Low level to the High level through the resistance R7 of the fixed voltage circuit 26.

[0070] Further, when the transistor Q3 of the constant-current electric door lock drive circuit 26 is controlled to the conductive state with the use of the control circuit 20 of the talk module 10 which forms the main entrance station 1, without supplying the power supply, for example, the power supply of low voltage such as 5V from the power supply circuit 27, the constant current of the small current value based on the direct current power supply, for example, DC 24 V from the common bus 3 is supplied to the electric door lock relay RY1 to make the electric door lock relay RY1 become the ON state so that the electric door lock switch SW1 is opened whereby the electric door lock 5 can be released without lowering the alternating current impedance of the common bus 3. Further, with the control circuit 20, even when the voltage level of the direct current power supply of the common bus 3 is changed, since the transistors Q3 absorbs the change width of the voltage level, the voltage applied to the electric door lock relay RY1 can be always made constant so that voltage which exceeds the specification is not generated.

[0071] Then, as shown in the block diagram of FIG. 1, when the visitor standing in the residential front door operates the call switch 6 to call the resident in the inside of the residence, the call signal is transmitted to the control circuit 40 of the residential master station 2.

[0072] Further, based on the call signal outputted from the call switch 6, the control circuit 40 of the residential master station 2 which detects the call operation of the visitor standing in the residential front door, as in the case of detecting the calling by selecting station by the visitor standing in the above-mentioned main entrance, controls the transistors Q6, Q7 of the piezoelectric element circuit 46 shown in the circuit block diagram of FIG. 2 respectively to the conductive state and the non-conductive state and supplies the constant current of the small electric current value based on the direct current power supply from the common bus 3, for example DC 24V to the piezoelectric element PD1. That is, the current is not supplied to the piezoelectric element PD1 from the power supply of the power supply circuit 47 such as the power supply of low level at 5 V. By alternately repeating the state of the piezoelectric element PD1 between the ON state and the OFF state, the call tone can be generated so that the calling from the visitor standing at the residential front door can be informed to the resident living in the residence which forms the selected station. Further, with the control circuit 20, even when the voltage level of the direct current power supply of the common bus 3 is changed, since the transistors Q6, Q7 absorb the change width of the voltage level, the voltage applied to the piezoelectric element PD1 can be always made constant so that voltage which exceeds the specification is not generated.

[0073] As can be clearly understood from the above description, according to the intercom system for mansion/apartment house of the present invention, by suppressing the respective impedance at the high region and the low region through the frequency characteristic circuit which is connected in parallel with the impedance increasing circuit of the bus controller, even when the frequency of the direct current power supply becomes high, the output impedance to the common bus can be increased up to the given impedance and, at the same time, the impedance increasing circuits respectively perform the constant-current operation due to the control performed by the fixed voltage circuits at the time of receiving the power supply from the bus controller at the main entrance station and at the residential master stations. Accordingly, even when the main entrance station, the residential master stations and the bus controller are connected to the common bus in parallel, the lowering of the alternating current impedance which the common bus has can be prevented.

[0074] Further, by connecting the speech circuits having the load resistances to the impedance increasing circuit of the talk module which forms the main entrance station and the impedance increasing circuits of respective residential master stations in series, it becomes possible to sufficiently cancel the feedback tone signals without receiving the influence of the alternating current impedance which the common bus has whereby the generation of the howling can be prevented.

[0075] Still further, the power supply to the constant-current electric door lock drive circuit of the talk module which forms the main entrance station and the power supply to the piezoelectric element circuits of the residential master stations which inform of the operation of the call switch based on the generation of the call tone are performed by supplying the constant current from the common bus which is assumed to take the small electric current value based on the direct-current power supply from the common bus while obviating the low-level voltage which is stabilized in the inside of the talk module and in the inside of the residential master stations. 

What is claimed is:
 1. An intercom system for mansion/apartment house which connects at least one main entrance station including a talk module for performing calling and talking and at least one switch module being connected to the talk module and having a call switch for performing selecting of a station, a bus controller for supplying a power to a common bus, and a plurality of residential master stations for performing calling and talking with the main entrance station to the common bus in parallel respectively, wherein: the bus controller comprises an impedance increasing circuit for increasing an output impedance to a high impedance, the talk module of the main entrance station comprises a speech circuit having a load resistance which is connected to the common bus, and each residential master station comprises a speech circuit having a load resistance which is connected to the common bus.
 2. An intercom system for mansion/apartment house according to claim 1, wherein the talk module of the main entrance station and the residential master stations are respectively provided with impedance increasing circuits for increasing input impedance at the standby state to a high impedance and the impedance increasing circuits are respectively provided with fixed voltage circuits.
 3. An intercom system for mansion/apartment house according to claim 1, wherein the impedance increasing circuit of the bus controller is provided with a frequency calibration circuit.
 4. An intercom system for mansion/apartment house according to claim 1, wherein the talk module of the main entrance station comprises a constant-current electric door lock drive circuit for driving an electric door lock circuit which locks and releases an electric door lock.
 5. An intercom system for mansion/apartment house according to claim 1, wherein the residential master station comprises a piezoelectric element circuit which generates a calling tone upon operation of a call switch which is installed at a residential front door. 